Drying process



Patented Mar. 25, 1941 UNITED STATES DRYING PROCESS William H. Pteiifer, Woodsidei N. Y., assignor to Gemex Company, Newark, N. 1., a corporation of New Jersey N 0 Drawing.

Application Januar 29,- 1940,

Serial No. 316,213

13 Claims.

This invention relates to a process of drying articles and more particularly to a process of drying wet metallic articles.

One of the objects of this invention is to provide a process for drying metal articles, which is simple, inexpensive and harmless in practice, and which does not necessitate chemical skill and experience. Another object is to provide a process of the above nature capable of spotlessly drying a wide variety of metal articles, regardless of their size or configuration, in a relatively short space of time. Other objects will be in part apparent and in part pointed out hereinafter.

While various chemical processes for drying metal articles have been attempted,the most widely used process is primary mechanical. Different kinds of plated metallic surfaces are often water scoured subsequent to the plating operation, and in order to dry such surfaces thoroughly without leaving residual spots thereon, the surfaces are agitated in finely divided sawdust or the like which absorbs the water from the metallic surfaces. While this process of drying is reasonably efi'ective where the surfaces being dried are of simple configuration or are fiat, it is time-consuming, necessitates bulky equipment, is not susceptible to any great measure of control, and, where the articles being dried are large, it is fatiguing and difficult to carry out. Sawdust drying of more complicated surfaces, i. e. surfaces or articles characterized by narrow grooves or channels, undercuts and the like, is of questionable effectiveness, as in many cases the sawdust particles are too large to enter the crevices and undercuts which are, of course, natural water traps; if the sawdust does enter such cavities it often becomes wedged therein. If the article is to be further treated, as by lacquering, for example, any sawdust clinging to the article subsequent to the drying operation spoils the lacquered surface and renders it more susceptible to cracking or peeling, in addition to detracting from the appearance of the surface. This is particularly true of brass, bronze or copper plated surfaces which are often lacquered to prevent tarnishing.

Removal of particles of the absorbent solid drying material, such as sawdust, has been attempted by brushing or by compressed air, both with indifferent success, however, as brushing tends to leave streaks, and drying by compressed air may create spots during the drying, it being difllcult to thoroughly filter the air blown against the surface.

I have found that if the metal article is thoroughly Wet with substances which arexapable of removing the water from the surfaces by solution or replacement thereof, and which are miscible with a chlorinated solvent, the amount a of water carried into the chlorinated solvent is so slight as probably to be thoroughly absorbed with such substances by the solvent. I believe this to-be true regardless of the fact that the water and the chlorinated solvent may be immiscible.

In the practice of my process, I first dip the water wet article into an organic liquid which is either miscible with water, or which is capable of replacing the water on the article. The organic liquid accordingly removes water from the article either by dissolving the water or by replacing it. This dissolution or replacement of the water probably occurs either because the water and the substances contained therein are uniformly dissolved in, and are therefore considerably diluted by, the organic liquid, or because the organic liquid has a greater affinity for the surface than has the water. If the organic liquid replaces the water on the surface, the water is dispersed uniformly in the main body of the liquid as a relatively finely divided supension. The uniform character of the suspension or mixture of the water in the organic liquid results, as preferably the metallic article is agitated during its immersion in the bath of organic liquid. Viewed in this light, the article has adhering to it a film of a uniform mixture or a suspension of water in the organic liquid in which the concentration of water is easily controllable below a workable maximum. .The extent to which the concentration of water in the organic liquid is permitted to increase depends on the extent to which the organic liquid-water mixture is to be removed from the article by subsequent treatment before final drying.

After immersion and preferably agitation of the article in the organic liquid, which will hereinafter be termed the primary bath, I transfer the article to a liquid that will hereinafter be termed the secondary bath, and this secondary bath is preferably a substance which is immiscible with water, but miscible with the abovenoted organic liquid, or primary bath, has a vapor density considerably greater than that of air, and is preferably non-inflammable for practical reasons, The article dipped in the secondary bath is preferably agitated during its immersion therein so as to uniformly mix the organic liquid and water which was carried over from the primary bath in the secondary bath. During this mixing action, there is apparently a. tendency of a portion of the water to be stripped or separated from the primary bath liquid. because I haveobserved that after continued immersion of successive articles in the secondary bath, globules of water may form on the surface thereof. This occurs. of course, only when the secondary bath liquid has a greater specific gravity than that of water. It should be noted,

however, that the substance which comprises the secondary bath may be immiscible with water, but miscible with the primary bath liquid, and at the same time have a specific gravity less than that'of water, in which event the globules of water would form at the bottom of the secondary bath.

During the immersion and preferably agitation of the article in the secondary bath, the primary bath liquid adhering initially to the article is uniformly dispersed through the secondary bath by reason of its miscibility therewith and usually causes the secondary bath to absorb the small amount of water carried into the secondary bath by the primary bath liquid. By reason of the stripping of the water, and its mechanical separation from the mixture, the water content in the mixture of primary and secondary bath liquids is limited. Hence, the solution of :primary and secondary bath liquids adhering to the article as it leaves the secondary bath contains but aslight amount of the p ry bath liquid and practically no water.

Preferably the temperatures of the primary and secondary bath treatments up to this point approximate room temperature, as for practical purposes I have found that the two baths are effective without being heated. In this connection, it might be noted that an increase in the temperature of the primary solvent facilitates its mixture with water, and accordingly expedites the process in point of time.

After immersion and agitation of the metal article in the secondary bath, the article may be removed and immersed in another bath of the secondary liquid, or a substantial equivalent thereto. The temperature of this latter bath, however, is maintained at its boiling point so that this bath gives off vapor, which is utilized in a manner which will be hereinafter described.

While the article is immersed in the hot bath it is preferably agitated for a short period of time, during which time the hot bath dissolves the mixture of primary and secondary bath liquids which adhered to the article upon its immersion in the hot bath. This mixture of adhering primary and secondary bath liquids and water, if any, carried thereby, is accordingly dispersed uniformly throughout the hot bath so that when the article is withdrawn from the hot bath, it is wet with practically unadulterated hot bath liquid.

The article is then passed through the vapor given off by the hot bath which being saturated removes the hot bath liquid which adhered to the article as it Was withdrawn from the hot bath, and after the article is withdrawn from the vapor, it emerges clean, bright, free from water, practically free of hot bath liquid, and with no evidence of streaks or spots.

The immersions, described above, may be multiplied as desired, 1. e. the treatment with the primary bath liquid may be a single dip, or may be any desired number of dips, the number of immersions depending primarily on the character of the article being dried. Or, the determinaas to the exact number of dips may be based on the cost of the primary bath liquid, the cost of removal therefrom of water, the relative volatility of the bath liquid, or on other factors such as apparatus design. The same may be true of the number of immersions in the secondary bath.

I have also found that, under certain circumstances, further variations of my process are practical. For example, I have found that relatively small and smooth articles may be transferred directly either from the cold secondary bath or occasionally from the primary bath directly to the vapor bath. This may be done if the amount of water in the mixture or suspension of water and primary or secondary bath liquid adhering to the article is so negligible as not to necessitate repeated dips in the primary and secondary baths,

and in the hot liquid bath.

As to the character of the primary bath liquid, I have found that the alcohols, such as methyl, ethyl, propyl or isopropyl and butyl m y be used with 'good results. I have also found that the ketones, such as acetone, ethyl and methyl ketone are satisfactory. I attain satisfactory results using esters, such as ethyl acetate, isopropyl acetate and butyl lactate. Still other primary liquids, such as dioxane, are effective. Preferably, these liquids are used cold, so as to minimize losses by volatilization. However, if suitable equipment is used, the temperature of the primary bath can be raised. Also, if multiple dips in the primary bath are indicated, one or more of the primary baths may be maintained at elevated temperatures.

As noted hereinabove, the secondary bath liquid and primary bath liquid are miscible, preferably in all proportions, but the secondary is immiscible with water. For example, as a secondary solvent, I have found it practical to use chlorinated solvents such as carbon tetrachloride, chloroform, trichlor ethylene, tetrachlorethylene, and other solvents of this nature. Infiammable substances, having the properties referred to above, may be used with proper safeguards. It is preferable that the secondary bath liquid be readily separable from the primary bath liquid and water, and should have a reasonable degree of chemical stability.

With use of substances of the kind and in the manner set forth above, I have found that metallic surfaces, such as gold, silver, brass, copper and chromium plate and others, may be quickly, inexpensively and spotlessly dried, under conditions amenable to the health and comfort of labor. I have also found that depending upon the number of baths of the primary bath liquid used, that the baths be arranged serially, and if found necessary, fresh liquid continuously fed into the last bath at such a rate that the water concentration thereof is maintained below a desired maximum. Or, if desired, fresh liquid may be fed into each 1 bath, and the overflow carried to a fractionating tower for separation of the water and bath liquid, the water being discarded, and the bath liquid returned to the system.

If it is found desirable to use a number of baths of the secondary bath liquid, these can be handled in a counter current manner similar to that described above in which the primary baths are handled, adding, of course, adequate means for separating the primary bath liquid from what water is carried therewith and from the secondary solvent. Inasmuch as it is known that boiling chlorinated solvents, such as described above, often causes the development of acidity, certain stabilizers or neutralizers can be provided for limiting the acidity of the secondary bath, as desired.

As the process herein described might be varied in different ways, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In the art of drying an article having a finished surface which is wet with water, the steps of immersing the article in a primary bath of an organic liquid solvent selected from the class consisting of the alcohols, ketones and esters, removing the article from the primary bath and immersing it in a secondary bath of an organic substance selected from the class consisting of the chlorinated solvents, removing the article from the secondary bath, immersing the article in a tertiary bath the temperature of which is maintained approximately at the boiling point thereof, said tertiary bath comprising a substance the properties of which are substantially similar to those of the secondary bath, withdrawing the article from the tertiary bath and passing the article through a body of vapor given off by a liquid similar in properties to that of the tertiary bath, and removing the dry article.

2. In the art of drying an article having a finished surface which is wet with a first fluid, the steps of immersing the wet article in a body of a second fluid which second fluid is capable of removal of said first fluid without attacking or reacting with said article, withdrawing the article from said second fluid, immersing the article in a third fluid immiscible with water but miscible with said first fluid which remains on the article, withdrawing the article from said third fluid, immersing the article in a fourth fluid the characteristics of which are the same or similar to the characteristics of said third fluid, and withdrawing the article from said fourth fluid.

3. In the art of drying water-wet articles, the steps of immersing the article in an alcohol, withdrawing the article from said alcohol, immersing the article in a chlorinated solvent the temperature of which is maintained approximately at room temperature, withdrawing the article from said chlorinated solvent, immersing the article in a boiling chlorinated solvent, withdrawing the article from the boiling chlorinated solvent, and passing the article through the vapor given off by said boiling chlorinated solvent.

4. In the art of drying an article having a finished surface which is wet with water, carrying on in the order named, the steps of thoroughly wetting the article with a liquid alcohol, thoroughly wetting the article with a chlorinated solvent, and treating the article with a hot chlorinated solvent.

5. In the art of drying an article having a finished surface which is wet with water, carrying on in the order named, the steps of thoroughly wetting the article with a liquid alcohol, and thereafter passing the article through a hot chlorinated solvent.

6. In the art of drying an article having a finished surface which is wet with water, carrying on in the order named, the steps of immersing the wet article in a body of a first fluid which is capable of removal of the water on the article by dilution or replacement without attacking or reacting with the article, withdrawing the article from said first fluid, immersing the article in a second fluid which is immiscible with water but miscible with said first fluid which remains on the article and which will not attack or react with said article, and withdrawing the article from said second fluid.

'7. In the art of drying articles having finished surfaces which are wet with water, carrying on in the order named, the steps of passing the articles through a body of an organic liquid solvent selected from the class consisting of the alcohols ketones and esters, and subsequently passing thl articles through a body of fiuidselected from th( classconsis-tiing of the chlorinated solvents.

8. In the art of drying articles having finishec surfaces which are wet with water, the steps 01 passing the articles through a bath consisting o: a substance miscible with water, passing the articles through a bath consisting of a substanci miscible with the substance of the first bath it all proportions, and passing the articles througl a bath of a substance similar to that of the second bath but which is maintained at its boiling point.

9. In the art of drying a water-wet article, thl steps of wetting the article with ethyl alcohol b1 passing the article through a. bath thereof ant agitating the article during its immersion in saii bath, withdrawing said article from said bath passing said article through a hot vaporized chlo rinated liquid in which said alcohol is soluble and withdrawing said article from said chlo rinated liquid.

10. In the art of drying an article having afln ished surface which is wet with water, the step: of immersing the article in a liquid solvent whicl is miscible with water, agitating said article i: said liquid, withdrawing said article from sail liquid, immersing said article in a hot organii chlorinated fluid which is miscible with sail liquid in all proportions, and withdrawing sail article from said fluid.

11. In the art of drying an article having a fin ished surface which is wet with water, the step of dissolving the water on said article by immer sion thereof in a liquid miscible with water bu which will not attack or react with said article dissolving said liquid and replacing the wate from the solution adhering to the article after it withdrawal from said liquid by immersing th article in a second liquid miscible with said flrs liquid and capable of evaporation from the arti cle without leaving a residue thereon, and evap orating the solution adhering to the article afte its withdrawal from said second liquid.

12. In the art of drying an article having a fin ished surface which is wet with water, the step of dissolving the water on said article by immer sion thereof in a liquid miscible with water bu which will not attack or react with said articli dissolving said liquid and replacing the wate from the solution adhering to the article afterit withdrawal from said liquid by immersing the ar ticle in a second liquid miscible with said firs liquid and maintained at its boiling point, an withdrawing the article from said second liqui into the vapor given off by said second liquid t evaporate any liquid adhering to the article.

13. In the art of drying an article having a fin ished surface which is wet with water, the step of dissolving the water on said article by immer sion thereof in a liquid miscible with water bu which will'not attack or react with said articli dissolving said liquid and replacing the wate from the solution adhering to the article after it withdrawal from said liquid by immersing th article in a second liquid miscible with said fir: liquid, and evaporating the solution adhering t the article after its withdrawal from said secon liquid in the presence of a vapor having char acteristics in liquid form similar to said secon liquid.

WILLIAM H. PFEIFFER.

CERTIFICATE OF CORRECTION Phat-amino. 2,2561%5. M- March 25, 19 4- 4 PFEIFFER.

iIt is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, second colmnn, line 51, claim 10, strike out the words in all proportions";

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent office.

Signed and sealed this 28th day of April, A. D. 19h2.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

